1. Field of the Invention
The present invention relates to a rotary joint for accomplishing an optical transmission of signals between a stationary part and a rotary part rotatably assembled to the stationary part.
2. Description of Related Art
As surveillance cameras devices built in an indoor ceiling etc., there are a number of surveillance camera devices that conduct surveillance at variable imaging directions while controlling a pan angle of a camera and its tilt angle, in widespread use. In common with many surveillance camera devices capable of controlling camera angles, a device's movable part rotatable in panning is connected with a stationary part built in a ceiling or the like through the intermediary of an electric camera-platform. That is, in the majority of surveillance cameras devices, the movable part having the camera equipped with a tilting mechanism for rotating the camera in the direction of tilting is attached to one part (movable part) of the electric camera-platform rotatable in the direction of pan, while the other part (immovable part) of the camera-platform is attached to the stationary part. In the so-constructed surveillance cameras device, image signals are generated from the camera mounted on the movable part. Next, the image signals are transmitted to the stationary part through the electric camera-platform. In the stationary part, image processing or conversion for output interface is applied on the image signals and subsequently, the so-processed image signals are outputted to an outside monitor, an image-signal recorder or the like.
There are many types of electronic camera-platform for the surveillance cameras device known in the prior art. As for the electronic camera-platform capable of swiveling the movable part in the direction of pan continuously, particularly, there is known an electronic camera-platform where a sliding contact between a slip ring and a brush constitutes a signal connection route for bridging over signals between a swivel part and a stationary part by. However, this kind of electronic camera-platform has a lot of shortcomings, for instance, unstable electrical contact between the slip ring and the brush caused by adhesion of oil slick and dusts, noise pollution accompanied with mechanical contact between the slip ring and the brush, deterioration in the performance of electrical contacting, etc. Particularly, there has arisen an occurrence of noise with the swivel movement in transmitting image signals and an occurrence of malfunctions in transmitting control signals for panning and tiling the camera. Additionally, such a transmission adopting mechanical contacts has a limited range of transmissible frequencies, so that it is impossible to transmit superfine image signals and high-speed data. For this reason, there has been desired appropriate connecting means that is capable of transmitting the image signals and data with high quality and at a high speed without deteriorating its transmission performance in spite of the long-term using.
Under the above circumference, a rotary optical coupling device for transmitting and receiving electric signals in non-contact manner is disclosed in Japanese Patent Publication Laid-open No. 2001-44940. In the publication, the rotary optical coupling device includes light emitting elements and light receiving elements in two pairs. In arrangement, the light receiving element on the stationary side and the light receiving element on the rotary side are arranged so as to oppose each other at the substantial center of a rotating axis of the device. Outside these light receiving elements, the light emitting elements are arranged so as not to overlap with the light receiving elements, respectively. In operation, the light emitting elements emit their light beams against respective centers of the mating light receiving elements obliquely.